1. Field of the Invention
The preset invention relates to a pressure-sensitive adhesive composition having antistatic ability, and an antistatic pressure-sensitive adhesive sheet and surface protecting film obtained by converting into a sheet or a tape using the composition. A pressure-sensitive adhesive sheet comprising the antistatic pressure-sensitive adhesive composition of the present invention is suitably used in plastic products on which static electricity is easily generated. Inter alia, in particular, they are useful as an antistatic pressure-sensitive adhesive sheet and surface protecting film which are used in fields disliking static electricity such as electronic instruments.
2. Description of the Related Art
A surface protecting film is generally used for the purpose of preventing a scratch or a stain generated at procession or conveyance of a subject to be protected by attaching the film via a pressure-sensitive adhesive coated on a protecting film side. For example, a panel of a liquid crystal display is formed by attaching an optical member such as a polarizing plate and a wavelength plate to a liquid crystal cell via an adhesive. A protecting film is attached to these optical members to be attached to a liquid crystal cell via a pressure-sensitive adhesive for the purpose of preventing a scratch or a stain.
And, at a stage at which a protecting film becomes unnecessary by attaching this optical member to a liquid crystal cell, a protecting film is removed by peeling. Generally, since a protecting film and an optical member are constructed of a plastic material, electrical insulating property is high, and static electricity is generated upon friction or peeling. Therefore, also when a protecting film is peeled from an optical member such as a polarizing plate, static electricity is generated. When a voltage is applied to a liquid crystal in the state where static electricity remains, orientation of a liquid crystal molecule is lost, and a defect of a panel is generated. Then, in order to prevent such the inconvenience, a surface protecting film is subjected to various antistatic treatments.
For example, a method of preventing electrification by adding one or more kinds of surfactants to a pressure-sensitive adhesive, and transferring surfactants to an adherend from a pressure-sensitive adhesive is disclosed (e.g. JP-A No. 9-165460). However, this invention is an invention in which a surfactant is transferred to an adherend by bleeding on a pressure-sensitive adhesive surface and, when attached to a protecting film, stain onto an adherend is not avoided. In addition, when an amount of a surfactant to be added is reduced in view of stain onto an adherend, sufficient antistatic ability is not obtained. Therefore, when a pressure-sensitive adhesive with a low-molecular surfactant added thereto is applied to a protecting film for an optical member, it is difficult to manifest sufficient antistatic without deteriorating optical property of an optical member.
In addition, a method for suppressing an antistatic agent from bleeding on a pressure-adhesive surface by adding an antistatic agent consisting of polyether polyol and an alkali metal salt to an acryl pressure-sensitive adhesive is disclosed (e.g. JP-A No. 6-128539). However, also in this method, bleeding of an antistatic agent is not avoided. As a result, it was found that, in the case where actually applied to a surface protecting film, when treatment is performed with long time or under a high temperature, there arises a problem that a surface protecting film is partially peeled off from an adherend by bleeding phenomenon.